1. Field of the Invention
The present invention relates to a liquid ejection head and a manufacturing method thereof, more particularly to a liquid ejection head constituted of at least lower electrodes, piezoelectric bodies and upper electrodes, which are successively arranged over pressure chambers connected to liquid ejection ports, and a manufacturing method thereof.
2. Description of the Related Art
Japanese Patent Application Publication No. 2002-370353 discloses a liquid spray head constituted of an upper electrode having the width Lu in the direction of arrangement of liquid chambers (pressure chambers), a piezoelectric body having the length Lp in the direction of arrangement of the liquid chambers, and a lower electrode having the width L1 in the direction of arrangement of the liquid chambers, in which the relationships between these dimensions are Lu≦Lp<L1.
Japanese Patent Application Publication No. 2003-025573 discloses a piezoelectric transducer for use in an ink jet print head which the piezoelectric transducer has an outer perimeter sized and positioned to overlap a chamber aperture (a pressure chamber).
Japanese Patent Application Publication No. 2003-165214 discloses an ink ejection head constituted of a pressure chamber having the breadth L in the breadthways direction, and a drive electrode having the width δ in the same direction as the breadth L, in which conditions of 0.1 mm≦L, and 0.29≦(δ/L)≦1 or optimum conditions of 0.57≦(δ/L)≦0.77, are satisfied.
Japanese Patent Application Publication No. 2004-351878 discloses an inkjet head in which the planar shape of an individual electrode is formed to a substantially similar shape to the planar shape of the opening of a recess part which forms a pressurization chamber (pressure chamber), and the surface area A1 of the individual electrode and the surface area A2 of the opening of the recess part are set in the range of: A2×0.6≦A1≦A2×0.9.
Japanese Patent Application Publication No. 11-034321 discloses an inkjet head in which a piezoelectric active region is formed to a smaller size than a corresponding pressurization chamber, in a planar direction parallel to the piezoelectric film, and is disposed in this planar direction at an interval from the perimeter edge of the pressurization chamber, throughout the whole circumference.
There are demands that the aspect ratio of the pressure chambers (when a pressure chamber has the length CWy and the breadth CWx, the aspect ratio of the pressure chamber is CWy/CWx) should be selectable appropriately in accordance with the required characteristics of the liquid ejection head. More specifically, if increased density in the nozzle arrangement in one row is pursued, for example, then it is desirable for the aspect ratio of the pressure chambers to be as high as possible. On the other hand, as the aspect ratio of the pressure chambers increases, the flow channel resistance inside the pressure chambers becomes greater. Hence, when pursuing high-frequency ejection of liquid of high viscosity, it is desirable, conversely, for the aspect ratio of the pressure chambers to be as close as possible to one.
Moreover, a liquid ejection head having high ejection efficiency is also sought. Further, a liquid ejection head which suffers little variation in ejection force between the nozzles is also sought. Furthermore, a liquid ejection head having high reliability, which suffers little variation in ejection volume or other defects over time, is also sought.
As shown in FIG. 14, the lengthwise direction of a pressure chamber 52 coincides with the ink flow direction. If electrodes 91 and 93, which face each other across a piezoelectric body 92, extend to positions in the vicinity of the edges of the pressure chamber 52, then a displacement profile 98 will not be a smooth and efficient displacement profile, a vibration mode having a high harmonic frequency will occur inside the pressure chamber 52, bubbles 99 will become more liable to collect and other adverse effects, such as decline in the ink ejection from the nozzles 51 and generation of residual vibrations, will arise.